1. Field of the Invention
The present invention generally relates to a suspension or solution having transition metal oxide, and more particularly to a suspension or solution having transition metal oxide for organic optoelectronic device, making method thereof, and applications.
2. Description of Related Art
The organic optoelectronic devices, such as organic solar cells (OSC), organic light emitting diodes (OLED), organic light sensors, and so on, have many advantages. For example, the organic optoelectronic devices can be lightweight, thin, large-area, flexible, and low-cost devices.
In order to increase the power conversion efficiency of the organic optoelectronic device, a buffer layer can be disposed between the organic layer and the electrode. For example, a thin layer composed of calcium or lithium fluoride can be disposed between the Al electrode and the organic layer. A buffer layer including PEDOT can be disposed between the transparent electrode and the organic layer so as to increase the power conversion efficiency.
However, Al electrode, calcium, or lithium fluoride is easy to be oxidized in air, and may cause the increased resistance of the device. Moreover, PEDOT is corrosive, and the transparent electrode will be damage by PEDOT easily.
In order to improve the problems described above, it has been reported that Al electrode is replaced by a high work-function metal which is used as a cathode, and transition metal oxides, such as vanadium oxide or tungsten oxide, are formed between the cathode and the organic layer for transporting or injecting holes effectively so as to increase the power conversion efficiency. Moreover, other transition metal oxide, such as zinc oxide, is not corrosive. The zinc oxide can be formed between the transparent electrode (anode) and the organic layer. The zinc oxide can be used as an electron transporting or injecting electrons layer for replacing PEDOT.
The transition metal oxide layers described above are usually formed by the vacuum evaporation process. The making cost is high, and it is difficult to produce a large-area device. Some transition metal oxide layers can be formed by the sol-gel method. It is possible to produce a large-area device by the sol-gel method. However, the sol-gel method includes the high temperature annealing treatment. The process temperature is usually higher than the glass transition temperature (Tg) of the organic material, may resulting in damaged organic layer.